This invention relates to the art of an exposing apparatus which exposes a light-sensitive material to perform image recording. More particularly, the invention relates to a multi-channel exposing apparatus capable of rapid recording of high-quality images using a liquid-crystal based spatial light modulating element.
Exposing apparatuses which scan and expose light-sensitive materials such as silver halide photographic materials and electrophotographic photoreceptors by means of recording light modulated in accordance with the image to be recorded, are commonly employed in various types of printers and copiers.
Most of the exposing apparatuses used today depend on light beam scanning for exposure, in which an optical beam modulated in accordance with the image to be recorded is deflected in a main scanning direction as the beam and the light-sensitive material are moved relative to each other in an auxiliary scanning direction perpendicular to the main scanning direction, whereby the light-sensitive material is scan exposed two-dimensionally to record an image (either latent or visible).
With the recent advances in image recording technology, it has become possible to record high-quality images at high speed by means of exposing apparatuses of such optical beam scanning type. However, imagewise exposure by means of optical beam scanning is limited in exposing speed and resolution and, particularly with large images, it is even more difficult to record high-quality images at high speed for the following reasons.
In imagewise exposure by optical beam scanning, a light beam modulated in accordance with the image to be recorded is deflected for scanning with an optical deflector such as a polygonal mirror or a galvanometric mirror. However, such optical beam scanning is theoretically limited in the resolution that can be attained and due to limiting factors such as the modulation (response) speed of the modulating element and the scanning precision of the optical deflector, it is impossible to achieve image recording with resolution higher than a certain value.
In order to provide higher resolution, the scanning speed has to be slowed down in conformity with the modulation speed of the optical modulator and this increases the image recording time. On the other hand, in order to realize high-speed recording, the resolution has to be lowered in conformity with the modulation speed.
The recording speed is also limited by the fact that exposure basically employs a single beam (in color image recording, one beam is used for each of R, G, and B exposing light).
As a further problem, the angle of deflection, or scan width, is limited, so in order to record large images, say, one of size A2, the pathlength of the optical beam has to be increased significantly, but then the exposing apparatus will unavoidably become bulky, causing considerable difficulty in recording larger images.
In addition, the optical beam scanning apparatus is costly since it requires expensive optics including an optical deflector, tilting compensation optics and an f.theta. lens. Particularly in the case where high-speed recording or the recording of larger images is desired, expensive optical elements of high precision or those of large size are required and a further increase in cost is unavoidable.